This application claims priority from German Application No. 199 56 131.1, filed on Nov. 23, 1999, the subject matter of which is hereby incorporated herein by reference.
1. Field of the Invention
The invention provides nucleotide sequences which encode the pfk gene and a process for the fermentative preparation of amino acids, in particular L-lysine, using coryneform bacteria in which the pfk gene is enhanced.
2. Background Information
Amino acids, in particular L-lysine, are used in human medicine and in the pharmaceuticals industry, but in particular in animal nutrition.
It is known that amino acids are prepared by fermentation from strains of coryneform bacteria, in particular Corynebacterium glutamicum. Because of their great importance, work is constantly being undertaken to improve the preparation processes. Improvements to the processes can relate to fermentation measures, such as, for example, stirring and supply of oxygen, or the composition of the nutrient media, such as, for example, the sugar concentration during the fermentation, or the working up to the product form by, for example, ion exchange chromatography, or the intrinsic output properties of the microorganism itself.
Methods of mutagenesis, selection and mutant selection are used to improve the output properties of these microorganisms. Strains which are resistant to antimetabolites, such as, for example, the lysine analogue S-(2-aminoethyl)-cysteine, or are auxotrophic for metabolites of regulatory importance and produce L-amino acids, such as, for example, L-lysine, are obtained in this manner.
Recombinant DNA techniques have also been employed for some years for improving Corynebacterium strains which produce amino acids, by amplifying individual amino acid biosynthesis genes and investigating the effects of such changes on the amino acid production. Review articles on this subject are to be found, inter alia, in Kinoshita (xe2x80x9cGlutamic Acid Bacteriaxe2x80x9d, in: Biology of Industrial Microorganisms, Demain and Solomon (Eds.), Benjamin Cummings, London, UK, 1985, 115-142), Hilliger (BioTec 2, 40-44 (1991)), Eggeling (Amino Acids 6:261-272 (1994)), Jetten and Sinskey (Critical Reviews in Biotechnology 15, 73-103 (1995)) and Sahm et al. (Annuals of the New York Academy of Science 782, 25-39 (1996)).
It is an object of the invention to provide new means for improved fermentative preparation of amino acids, in particular L-lysine.
Amino acids, in particular L-lysine, are used in human medicine, in the pharmaceuticals industry and in particular in animal nutrition. There is therefore a general interest in providing new improved processes for the preparation of amino acids, in particular L-lysine.
When L-lysine or lysine are mentioned in the following, not only the base but also the salts, such as, for example, lysine monohydrochloride or lysine sulfate, are also meant.
The invention provides an isolated polynucleotide from coryneform bacteria, comprising a polynucleotide sequence chosen from the group consisting of
a) a polynucleotide which is at least 70% identical to a polynucleotide which encodes a polypeptide which comprises the amino acid sequence of SEQ ID NO:2,
b) a polynucleotide which encodes a polypeptide which comprises an amino acid sequence which is at least 70% identical to the amino acid sequence of SEQ ID NO:2,
c) a polynucleotide which is complementary to the polynucleotides of a) or b), and
d) a polynucleotide comprising at least 15 successive nucleotides of the polynucleotide sequence of a), b) or c).
In a preferred embodiment, the invention also provides the polynucleotide with the features described above, preferably being a DNA which is capable of replication, comprising:
(i) the nucleotide sequence shown in SEQ ID NO:1, or
(ii) at least one sequence which corresponds to sequence (i) within the range of the degeneration of the genetic code, or
(iii) at least one sequence which hybridizes with the sequence complementary to sequence (i) or (ii), and optionally
(iv) sense mutations of neutral function in (i).
The invention also provides
a polynucleotide with the aforementioned features, comprising the nucleotide sequence as shown in SEQ ID NO:1,
a polynucleotide with the aforementioned features, which encodes a polypeptide which comprises the amino acid sequence as shown in SEQ ID NO:2,
a vector containing the polynucleotide with features a)-d) above, in particular a shuttle vector or plasmid vector
and coryneform bacteria serving as the host cell, which contain the vector.
The invention also provides polynucleotides which substantially comprise a polynucleotide sequence, which are obtainable by screening by means of hybridization of a corresponding gene library, which comprises the complete gene with the polynucleotide sequence corresponding to SEQ ID NO:1, with a probe which comprises the sequence of the polynucleotide mentioned, according to SEQ ID no. 1 or a fragment thereof, and isolation of the DNA sequence mentioned.
Polynucleotide sequences according to the invention are suitable as hybridization probes for RNA, cDNA and DNA, in order to isolate, in the full length, CDNA which code for phosphofructokinase and to isolate those cDNA or genes which have a high similarity of sequence with that of the phosphofructokinase gene.
Polynucleotide sequences according to the invention are furthermore suitable as primers for the preparation of DNA of genes which code for phosphofructokinase by the polymerase chain reaction (PCR).
Such oligonucleotides which serve as probes or primers comprise at least 30, preferably at least 20, very particularly preferably at least 15 successive nucleotides. oligonucleotides which have a length of at least 40 or 50 nucleotides are also suitable.
xe2x80x9cIsolatedxe2x80x9d means separated from its natural environment.
xe2x80x9cPolynucleotidexe2x80x9d generally relates to polyribonucleotides and polydeoxyribonucleotides, wherein the RNA or DNA may be modified or unmodified.
xe2x80x9cPolypeptidesxe2x80x9d is understood as meaning peptides or proteins which comprise two or more amino acids bonded via peptide bonds.
The polypeptides according to the invention include a polypeptide according to SEQ ID NO:2, in particular those with the biological activity of phosphofructokinase, and also those which are at least 70% identical to the polypeptide according to SEQ ID NO:2, and preferably are at least 80% identical, and most preferably 90% to 95% identical to the polypeptide according to SEQ ID NO:2 and have the activity mentioned.
The invention also provides a process for the fermentative preparation of amino acids, in particular L-lysine, using coryneform bacteria which in particular already produce an amino acid, and in which the nucleotide sequences which code for the pfk gene are enhanced, in particular over-expressed.
The term xe2x80x9cenhancementxe2x80x9d in this connection describes the increase in the intracellular activity of one or more enzymes in a microorganism which are encoded by the corresponding DNA, for example by increasing the number of copies of the gene or genes, using a potent promoter or using a gene which encodes a corresponding enzyme having a high activity, and optionally combining these measures.
The microorganisms provided by the present invention can be used to prepare L-amino acids, in particular L-lysine, from glucose, sucrose, lactose, fructose, maltose, molasses, starch, cellulose or from glycerol and ethanol. They can be representatives of coryneform bacteria, in particular of the genus Corynebacterium. Of the genus Corynebacterium, the species Corynebacterium glutamicum, which is known among experts for its ability to produce L-amino acids, is particularly useful.
Suitable strains of the genus Corynebacterium, in particular of the species Corynebacterium glutamicum, are, for example, the known wild-type strains
Corynebacterium glutamicum ATCC13032
Corynebacterium acetoglutamicum ATCC15806
Corynebacterium acetoacidophilum ATCC13870
Corynebacterium thermoaminogenes FERM BP-1539
Corynebacterium melassecola ATCC17965
Brevibacterium flavum ATCC14067
Brevibacterium lactofermentum ATCC13869 and
Brevibacterium divaricatum ATCC14020
and L-lysine-producing mutants or strains prepared therefrom, such as, for example
Corynebacterium glutamicum FERM-P 1709
Brevibacterium flavum FERM-P 1708
Brevibacterium lactofermentum FERM-P 1712
Corynebacterium glutamicum FERM-P 6463
Corynebacterium glutamicum FERM-P 6464 and
Corynebacterium glutamicum DSM5715.
The inventors have succeeded in isolating the new pfk gene of C. glutamicum which codes for the enzyme phosphofructokinase.
To isolate the pfk gene or also other genes of C. glutamicum, a gene library of this microorganism is first constructed in E. coli. The construction of gene libraries is described in generally known textbooks and handbooks. The textbook by Winnacker: Gene und Klone, Eine Einfxc3xchrung in die Gentechnologie [Genes and Clones, An Introduction to Genetic Engineering] (Verlag Chemie, Weinheim, Germany, 1990) or the handbook by Sambrook et al.: Molecular Cloning, A Laboratory Manual (Cold Spring Harbor Laboratory Press, 1989) may be mentioned as examples. A well-known gene library is that of the E. coli K-12 strain W3110 constructed in xcex vectors by Kohara et al. (Cell 50, 495-508 (1987)). Bathe et al. (Molecular and General Genetics, 252:255-265, 1996) describe a gene library of C. glutamicum ATCC13032, which was constructed with the aid of the cosmid vector SuperCos I (Wahl et al., 1987, Proceedings of the National Academy of Sciences USA, 84:2160-2164) in the E. coli K-12 strain NM554 (Raleigh et al., 1988, Nucleic Acids Research 16:1563-1575). Bxc3x6rmann et al. (Molecular Microbiology 6(3), 317-326)) (1992)) in turn describe a gene library of C. glutamicum ATCC13032 using the cosmid pHC79 (Hohn and Collins, Gene 11, 291-298 (1980)). To prepare a gene library of C. glutamicum in E. coli it is also possible to use plasmids such as pBR322 (Bolivar, Life Sciences, 25, 807-818 (1979)) or pUC9 (Vieira et al., 1982, Gene, 19:259-268). Suitable hosts are, in particular, those E. coli strains which are restriction- and recombination-defective. An example of these is the strain DHxcex1mcr, which has been described by Grant et al. (Proceedings of the National Academy of Sciences USA, 87 (1990) 4645-4649). The long DNA fragments cloned with the aid of cosmids can then in turn be subcloned in the usual vector suitable for sequencing and then sequenced, as is described, for example, by Sanger et al. (Proceedings of the National Academy of Sciences of the United States of America, 74:5463-5467, 1977).
The new DNA sequence of C. glutamicum which encodes the pfk gene and which, as SEQ ID NO:1, is a constituent of the present invention, was obtained in this manner. The amino acid sequence of the corresponding protein has furthermore been derived from the present DNA sequence by the methods described above. The resulting amino acid sequence of the pfk gene product is shown in SEQ ID NO:2.
Coding DNA sequences which arise from SEQ ID NO:1 as a result of the degeneracy of the genetic code are also a constituent of the invention. In the same way, DNA sequences which hybridize with SEQ ID NO:1 or parts of SEQ ID NO:1 are a constituent of the invention. Conservative amino acid exchanges, such as, for example, the exchange of glycine for alanine or of aspartic acid for glutamic acid in proteins, are furthermore known among experts as xe2x80x9csense mutationsxe2x80x9d which do not lead to a fundamental change in the activity of the protein, i.e. are of neutral function. It is furthermore known that changes on the N and/or C terminus of a protein cannot substantially impair or can even stabilize the function thereof. Information in this context can be found by the expert, inter alia, in Ben-Bassat et al. (journal of Bacteriology 169:751-757 (1987)), in O""Regan et al. (Gene 77:237-251 (1989)), in Sahin-Toth et al. (Protein Sciences 3:240-247 (1994)), in Hochuli et al. (Bio/Technology 6:1321-1325 (1988)) and in known textbooks of genetics and molecular biology. Amino acid sequences which result in a corresponding manner from SEQ ID NO:2 are also a constituent of the invention.
In the same way, DNA sequences which hybridize with SEQ ID NO:1 or portions of SEQ ID NO:1 are a constituent of the invention. Finally, DNA sequences which are prepared by the polymerase chain reaction (PCR) using primers which result from SEQ ID NO:1 are a constituent of the invention. Such oligonucleotides typically have a length of at least 15 nucleotides.
Instructions for identifying DNA sequences by means of hybridization can be found by the expert, inter alia, in the handbook xe2x80x9cThe DIG System Users Guide for Filter Hybridizationxe2x80x9d from Boehringer Mannheim GmbH (Mannheim, Germany, 1993) and in Liebl et al. (International Journal of Systematic Bacteriology (1991) 41: 255-260). Instructions for amplification of DNA sequences with the aid of the polymerase chain reaction (PCR) can be found by the expert, inter alia, in the handbook by Gait: Oligonucleotide synthesis: a practical approach (IRL Press, Oxford, UK, 1984) and in Newton and Graham: PCR (Spektrum Akademischer Verlag, Heidelberg, Germany, 1994).
The inventors have found that coryneform bacteria produce amino acids, in particular L-lysine, in an improved manner after over-expression of the pfk gene.
To achieve over-expression, the number of copies of the corresponding genes can be increased, or the promoter and regulation region or the ribosome binding site upstream of the structural gene can be mutated. Expression cassettes which are incorporated upstream of the structural gene act in the same way. By inducible promoters, it is additionally possible to increase the expression in the course of fermentative L-lysine production. The expression is likewise improved by measures to prolong the life of the m-RNA. Furthermore, the enzyme activity is also increased by preventing the degradation of the enzyme protein. The genes or gene constructions can either be present in plasmids with a varying number of copies, or can be integrated and amplified in the chromosome. Alternatively, an over-expression of the genes in question can furthermore be achieved by changing the composition of the media and the culture procedure.
Instructions in this context can be found by the expert, inter alia, in Martin et al. (Bio/Technology 5, 137-146 (1987)), in Guerrero et al. (Gene 138, 35-41 (1994)), Tsuchiya and Morinaga (Bio/Technology 6, 428-430 (1988)), in Eikmanns et al. (Gene 102, 93-98 (1991)), in European Patent Specification EPS 0 472 869, in U.S. Pat. No. 4,601,893, in Schwarzer and PUhler (Bio/Technology 9, 84-87 (1991), in Reinscheid et al. (Applied and Environmental Microbiology 60, 126-132 (1994)), in LaBarre et al. (Journal of Bacteriology 175, 1001-1007 (1993)), in Patent Application WO 96/15246, in Malumbres et al. (Gene 134, 15-24 (1993)), in Japanese Laid-Open Specification JP-A-10-229891, in Jensen and Hammer (Biotechnology and Bioengineering 58, 191-195 (1998)), in Makrides (Microbiological Reviews 60:512-538 (1996)) and in known textbooks of genetics and molecular biology.
By way of example, the pfk gene according to the invention was over-expressed with the aid of plasmids.
Suitable plasmids are those which are replicated in coryneform bacteria. Numerous known plasmid vectors, such as, for example, pZ1 (Menkel et al., Applied and Environmental Microbiology (1989) 64: 549-554), pEKEx1 (Eikmanns et al., Gene 102:93-98 (1991)) or pHS2-1 (Sonnen et al., Gene 107:69-74 (1991)) are based on the cryptic plasmids pHM1519, pBL1 or pGA1. Other plasmid vectors, such as, for example, those based on pCG4 (U.S. Pat. No. 4,489,160) or pNG2 (Serwold-Davis et al., FEMS Microbiology Letters 66, 119-124 (1990)), or pAG1 (U.S. Pat. No. 5,158,891) can be used in the same manner.
Plasmid vectors which are furthermore suitable are those with the aid of which the process of gene amplification by integration into the chromosome can be used, as has been described, for example, by Reinscheid et al. (Applied and Environmental Microbiology 60, 126-132 (1994)) for duplication or amplification of the hom-thrB operon. In this method, the complete gene is cloned in a plasmid vector which can replicate in a host (typically E. coli), but not in C. glutamicum. Possible vectors are, for example, pSUP301 (Simon et al., Bio/Technology 1, 784-791 (1983)), pKl8mob or pKl9mob (Schxc3xa4fer et al., Gene 145, 69-73 (1994)), pGEM-T (Promega corporation, Madison, Wis., USA), pCR2.1-TOPO (Shuman (1994). Journal of Biological Chemistry 269:32678-84; U.S. Pat. No. 5,487,993), pCR(copyright)Blunt (Invitrogen, Groningen, Holland; Bernard et al., Journal of Molecular Biology, 234: 534-541 (1993)) or pEMI (Schrumpf et al, 1991, Journal of Bacteriology 173:4510-4516). The plasmid vector which contains the gene to be amplified is then transferred into the desired strain of C. glutamicum by conjugation or transformation. The method of conjugation is described, for example, by Schxc3xa4fer et al. (Applied and Environmental Microbiology 60, 756-759 (1994)). Methods for transformation are described, for example, by Thierbach et al. (Applied Microbiology and Biotechnology 29, 356-362 (1988)), Dunican and Shivnan (Bio/Technology 7, 1067-1070 (1989)) and Tauch et al. (FEMS Microbiological Letters 123, 343-347 (1994)). After homologous recombination by means of a xe2x80x9ccross overxe2x80x9d event, the resulting strain contains at least two copies of the gene in question.
In addition, it may be advantageous for the production of amino acids, in particular L-lysine, to enhance or over-express one or more enzymes of the particular biosynthesis pathway, of glycolysis, of anaplerosis, of the citric acid cycle or of amino acid export, in addition to the pfk gene.
Thus, for example, for the preparation of L-lysine, one or more genes chosen from the group consisting of
the dapA gene which encodes dihydrodipicolinate synthase (EP-B 0 197 335), or
the gap gene which encodes glyceraldehyde 3-phosphate dehydrogenase (Eikmanns (1992), Journal of Bacteriology 174:6076-6086), or
the tpi gene which encodes triose phosphate isomerase (Eikmanns (1992), Journal of Bacteriology 174:6076-6086), or
the pgk gene which encodes 3-phosphoglycerate kinase(Eikmanns (1992), Journal of Bacteriology 174:6076-6086), or
the pyc gene which encodes pyruvate carboxylase(Eikmanns (1992), Journal of Bacteriology 174:6076-6086), or
the lysE gene which encodes lysine export (DE-A-195 48 222)
can be over-expressed at the same time.
For the production of amino acids, in particular L-lysine, it may furthermore be advantageous to attenuate, in addition to the pfk gene,
the pck gene which encodes phosphoenol pyruvate carboxykinase (DE 199 50 409.1, DSM 13047) and/or
the pgi gene which encodes glucose 6-phosphate isomerase (US 09/396,478, DSM 12969)
at the same time.
In addition to over-expression of the pfk gene it may furthermore be advantageous, for the production of amino acids, in particular L-lysine, to eliminate undesirable side reactions, (Nakayama: xe2x80x9cBreeding of Amino Acid Producing Micro-organismsxe2x80x9d, in: Overproduction of Microbial Products, Krumphanzl, Sikyta, Vanek (eds.), Academic Press, London, UK, 1982).
The microorganisms prepared according to the invention can be cultured continuously or discontinuously in the batch process (batch culture) or in the fed batch (feed process) or repeated fed batch process (repetitive feed process) for the purpose of production of amino acids, in particular L-lysine. A summary of known culture methods is contained in the textbook by Chmiel (Bioprozesstechnik 1. Einfxc3xchrung in die Bioverfahrenstechnik [Bioprocess Technology 1. Introduction to Bioprocess Technology (Gustav Fischer Verlag, Stuttgart, 1991)) or in the textbook by Storhas (Bioreaktoren und periphere Einrichtungen [Bioreactors and Peripheral Equipment] (Vieweg Verlag, Braunschweig/Wiesbaden, 1994)).
The culture medium to be used must meet the requirements of the particular strains in a suitable manner. Descriptions of culture media for various microorganisms are contained in the handbook xe2x80x9cManual of Methods for General Bacteriologyxe2x80x9d of the American Society for Bacteriology (Washington D.C., USA, 1981). Sugars and carbohydrates, such as, for example, glucose, sucrose, lactose, fructose, maltose, molasses, starch and cellulose, oils and fats, such as, for example, soya oil, sunflower oil, groundnut oil and coconut fat, fatty acids, such as, for example, palmitic acid, stearic acid and linoleic acid, alcohols, such as, for example, glycerol and ethanol, and organic acids, such as, for example, acetic acid, can be used as the source of carbon. These substances can be used individually or as a mixture. Organic nitrogen-containing compounds, such as peptones, yeast extract, meat extract, malt extract, corn steep liquor, soya bean flour and urea, or inorganic compounds, such as ammonium sulfate, ammonium chloride, ammonium phosphate, ammonium carbonate and ammonium nitrate, can be used as the source of nitrogen. The sources of nitrogen can be used individually or as a mixture. Phosphoric acid, potassium dihydrogen phosphate or dipotassium hydrogen phosphate or the corresponding sodium-containing salts can be used as the source of phosphorus. The culture medium must furthermore comprise salts of metals, such as, for example, magnesium sulfate or iron sulfate, which are necessary for growth. Finally, essential growth substances, such as amino acids and vitamins, can be employed in addition to the abovementioned substances. Suitable precursors can moreover be added to the culture medium. The starting substances mentioned can be added to the culture in the form of a single batch, or can be fed in during the culture in a suitable manner.
Basic compounds, such as sodium hydroxide, potassium hydroxide, ammonia or aqueous ammonia, or acid compounds, such as phosphoric acid or sulfuric acid, can be employed in a suitable manner to control the pH. Antifoams, such as, for example, fatty acid polyglycol esters, can be employed to control the development of foam. Suitable substances having a selective action, such as, for example, antibiotics, can be added to the medium to maintain the stability of plasmids. To maintain aerobic conditions, oxygen or oxygen-containing gas mixtures, such as, for example, air, are introduced into the culture. The temperature of the culture is usually 20xc2x0 C. to 45xc2x0 C., and preferably 25xc2x0 C. to 40xc2x0 C. Culturing is continued until a maximum of lysine has formed. This target is usually reached within 10 hours to 160 hours.
The analysis of L-lysine can be carried out by anion exchange chromatography with subsequent ninhydrin derivatization, as described by Spackman et al. (Analytical Chemistry, 30, (1958), 1190).
The process according to the invention is used for the fermentative preparation of amino acids, in particular L-lysine